This invention relates to casting of components from semi-solid metals and more particularly to casting components from semi-solid metal removed from a bath of semi-solid metal.
Manufacturers of metallic components have long recognized the advantages of die casting components which are adaptable to fabrication by that process. The advantages of die casting components from semi-solid (or thixotropic) metals are also well documented and include, but are not limited to, the creation of finished heat-treatable components that are less porous and exhibit a more homogeneous structure than components cast from molten metal.
Reference is made to a number of prior art references as follows:
U.S. Patents
1. U.S. Pat. No. 4,709,746, Process and Apparatus for Continuous Slurry Casting, to Young et al.
2. U.S. Pat. No. 5,313,815, Apparatus and Method for Producing Shaped Metal Parts Using Continuous Heating to Nichting et al.
3. U.S. Pat. No. 4,565,241, Process for Preparing a Slurry Structured Metal Composition, to Young.
4. U.S. Pat. No. 5,464,053, Process for Producing Rheocast Ingots, Particularly From which To Produce High-Mechanical-Performance Die Castings, to Moschini.
5. U.S. Pat. No. 5,381,847, Vertical Casting Process, to Ashok et al.
6. U.S. Pat. No. 5,375,645, Apparatus and Process for Producing Shaped Articles From Semisolid Metal Preforms, to Breuker et al.
7. U.S. Pat. No. 5,287,719, Method of Forming Semi-Solidified Metal Composition, to Moritaka et al.
8. U.S. Pat. No. 5,219,018, Method of Producing Thixotropic Metallic Products by Continuous Casting. With Polyphase Current Electromagnetic Agitation, to Meyer.
9. U.S. Pat. No. 5,178,204, Method and Apparatus for Rheocasting, to Kelly et al.
10. U.S. Pat. No. 5,110,547, Process and Apparatus for the Production of Semi-solidified Metal Composition, to Kiuchi et al.
11. U.S. Pat. No. 4,964,455, Method of Producing Thixotropic Metallic Products by Continuous Casting, to Meyer.
12. U.S. Pat. No. 4,874,471, Device for Casting a Metal in the Pasty Phase, to Wilmotte.
13. U.S. Pat. No. 4,804,034, Method of Manufacture of a Thixotropic Deposit, to Leathham et al.
14. U.S. Pat. No. 4,687,042, Method of Producing Shaped Metal Parts, to Young.
15. U.S. Pat. No. 4,580,616, Method and Apparatus for Controlled Solidification of Metals, to Watts.
16. U.S. Pat. No. 4,345,637, Method for Forming High Fraction Solid Compositions by Die Casting, to Flemings et al.
17. U.S. Pat. No. 4,108,643, Method for Forming High Fraction Solid Metal Compositions and Composition Therefor, to Flemings et al.
18. U.S. Pat. No. 3,902,544, Continuous Process for Forming an Alloy Containing Non-Dendritic Primary Solids, to Flemings et al.
19. U.S. Pat. No. 5,211,216, Casting Process, to Drury et al.
20. U.S. Pat. No. 3,948,650, Composition and Methods for Preparing Liquid-Solid Alloys for Casting and Casting Methods Employing the Liquid-Solid Alloys, to Flemings et al.
21. U.S. Pat. No. 3,954,455, Liquid-Solid Alloy Composition, to Flemings et al.
22. U.S. Pat. No. 4,972,899, Method and Apparatus for Casting Grain Refined Ingots, to Tungatt.
23. U.S. Pat. No. 4,577,676, Method and Apparatus for Casting Ingot with Refined Grain Structure, to Watson.
24. U.S. Pat. No. 4,231,664, Method and Apparatus for Combined High Speed Horizontal and High Speed Vertical Mixing of Chemically Bonded Foundry Sand, to Flock.
25. U.S. Pat. No. 4,506,982, Apparatus for Blending Viscous Liquids With Particulate Solids, to Smithers et al.
26. U.S. Pat. No. 4,469,444, Mixing and Degassing Apparatus for Viscous Substances, to Gmeiner et al.
27. U.S. Pat. No. 5,037,209, Apparatus for the Mixing of Fluids, in Particular. Pasty Media and a Process for its Operation, to Wyss.
28. U.S. Pat. No. 4,893,941, Apparatus for Mixing Viscous Liquids in a Container, to Wayte.
29. U.S. Pat. No. 4,397,687, Mixing Device and Method for Mixing Molten Metals, to Bye.
Related Articles
30. Rheocasting Processes, Flemings, M. C., Riek, R. G., and Young, K. P. xe2x80x9cInternational Cast Metals Journalxe2x80x9d, vol. 1, No. 3, September 1976, pp. 11-22.
31. Die Casting Partially Solidified High Copper Content Alloys, Fascetta, E. F., Riek, R. G., Mehrabian, R., and Flemings, M. C. xe2x80x9cCast Metals Research Journalxe2x80x9d, Vol. 9, No. 4, December 1973, pp. 167-171.
The above references teach the general concepts involved and benefits of forming metallic components from semi-solid metals. The references also teach the standard techniques used for die casting in general and for die casting components from semi-solid metal. Also included are references teaching various methods of stirring and agitating semi-solid materials. All of the references, and the references cited therein, are incorporated herein for purpose of establishing the methods and procedures available for processing semi-solid metals and die casting components and methods.
Most previous methods and devices for die casting components from semi-solid metals used cylindrical slugs cut from solid bars, or billets, preformed with a semi-solid microstructure. These billets were heated to cause them to return to a semi-solid state prior to being forced under extremely high pressure (typically on the order of 16,000-30,000 psi (2.32-4.35 Pa)) into casting molds. These billets are susceptible to surface oxidation allowing oxidized material to be incorporated into the final component. Also, this process requires that metal be heated to a semi-solid state, the billet be cast and cooled, inventoried, cut to length, possibly shipped, and finally reheated prior to casting of the final component.
The present invention provides a device and method whereby a bath of stable, constantly agitated, temperature controlled, semi-solid metal is maintained in a reservoir and delivered in its original semi-solid state to a die casting machine ready for immediate casting into a final component. The transfer may be accomplished through a heated suction tube and temperature controlled charge sleeve by vacuum ladling. The semi-solid metal being transferred is pressed into the die cavity by a plunger tip providing a vent path to break the vacuum formed during ladling to allow semi-solid metal in the suction tube to return to the bath during the pressing process. Thus a readily available bath of stable, homogenous, temperature controlled semi-solid metal is provided in a die-casting environment which may be delivered on demand in its semi-solid form to mold cavities of die-casting presses for fabrication of metallic components with enhanced performance characteristics.
According to the present invention an apparatus for delivering heated metal to a die casting device having at least one cavity, a vacuum gate, and a metal feed gate includes a source of molten metal maintained at a predetermined temperature range above the temperature at which it will begin to solidify, a vessel containing the metal in a semi-solid state wherein up to about 45% of the metal is suspended as particles in a fluid fraction of the metal, a heated suction tube, a shot sleeve in metal flow communication with the vessel through the heated suction tube and also in communication with the cavity through the metal feed gate, a plunger reciprocally disposed in the sleeve to force semi-solid metal in the sleeve under pressure into the cavity, and a vacuum source communicating with the vacuum gate, cavity, feed gate and shot sleeve to draw semi-solid metal from the temperature controlled vessel through the heated suction tube into the sleeve in a position to be forced by the plunger into the die. The vessel includes a bottom, a side wall, and a top, and the apparatus may include an agitator disposed in the vessel and a heater positioned to deliver heat to semi-solid metal in the vessel through the bottom of the vessel. The bottom of the vessel may include an independently dimensioned heating chamber in metal flow communication with the semi-solid metal in the vessel through the bottom of the vessel and the heater may be positioned to heat metal in the heating chamber. The heater may be an induction heater. The agitator may be positioned in the vessel to promote mixing of metal in the heating chamber with the semi-solid metal in the vessel. The shot sleeve may be jacketed and a fluid may be circulated through the jacket. The apparatus may include a delivery means for delivering predetermined volumes of molten metal from the source of molten metal to the vessel. The suction tube for delivering the semi-solid metal to the heated shot sleeve may extend upwardly from the surface of semi-solid metal in the vessel.
According to another aspect of the present invention, an improved vessel for holding and maintaining a semi-solid metal in an isothermal state for use in casting includes a bottom, side wall, and top, an agitator, and a heater located to deliver heat to the semi-solid metal in the vessel through the bottom of the vessel. The bottom of the vessel may include an independently dimensioned heating chamber in metal flow communication with semi-solid metal in the vessel through the bottom of the vessel with the heater positioned to heat metal in the heater chamber. The heater may be an induction heater. The vessel may include an agitator positioned to promote mixing of metal in the heating chamber with the stirred semi-solid metal in the vessel.
According to yet another aspect of the invention a die casting process wherein a semi-solid metal is driven from a charge sleeve by a plunger into a die is improved by including the step of heating the charge sleeve. The charge sleeve may be jacketed and a fluid may be circulated through the jacket.
According to another aspect of the invention, a method for die casting metal alloy from a source of alloy maintained in a semi-solid state includes the steps of providing a die casting press having a mold cavity for receiving the metal to be cast and chilling the metal to a solid form, providing a vessel of molten metal having a bottom and a side, lowering the temperature of the molten metal to a level at which the metal will begin to solidify, stirring the metal and controlling the temperature to maintain the metal at an isothermal state containing solid particles of metal and molten metal, wherein controlling the temperature is accomplished by heating through the bottom of the vessel and wherein cooling of the metal is in part through the side of the vessel, and wherein the stirring includes shearing of solidifying metal from the sides of the vessel, whereby the metal in the vessel is maintained in a stable semi-solid condition with constant stirring and temperature control. The step of periodically withdrawing controlled amounts of metal from the vessel and transferring the metal to the mold cavity for casting through a suction tube may be included. The temperature of the withdrawn metal may be controlled during the transferring step. Controlled amounts of molten metal may be periodically added to the vessel to replace each withdrawn amount of metal. The metal suspended in the suction tube may be allowed to return to the bath during casting of a component.
According to yet another aspect of the present invention an apparatus for delivering heated metal to a die casting device having at least a pair of dies forming at least one cavity therebetween, a vacuum gate, and a metal feed gate for the manufacture of molded metal castings includes a vessel having temperature control mechanisms and agitators for holding a reservoir of semi-solid metal, a system for delivering molten metal to the vessel, a transfer system to deliver semi-solid metal from the vessel to the die cast mold in the semi-solid state, and a heating chamber in fluid communication with the vessel. The apparatus may include regulators for controlling the amount of semi-solid metal withdrawn from the vessel and the amount of molten metal added to the vessel. The transfer system may include mechanical ladling or vacuum ladling and may also include a suction tube with a heater. The apparatus may include a suction tube in fluid communication with a shot sleeve and a plunger which seals the shot sleeve during vacuum ladling to allow semi-solid metal to be drawn into the shot sleeve and suspended in the suction tube prior to pressing the material into the mold cavity and which creates a vent path during the pressing process allowing metal previously suspended in the suction tube to return to the metal bath. The apparatus may also include an induction heater for heating metal within the heating chamber. The vessel may have a volume substantially greater than the volume of semi-solid metal required to fabricate a component by die casting.
According to the present invention, an apparatus for delivering heated metal to a die casting device having at least a pair of dies forming at least one cavity therebetween, a vacuum gate, and a metal feed gate for the manufacture of molded metal castings includes a vessel for holding a reservoir of semi-solid metal, a suction tube in fluid communication with the reservoir, and a charge sleeve in fluid communication with the cavity and the suction tube. The charge sleeve includes an aperture in which the suction tube is received to form a junction, the aperture is formed to reduce the surface area of the charge sleeve in the junction. The suction tube may include a beveled end received in the aperture. The suction tube may be non-metallic. The charge sleeve may include a countersink formed in the aperture.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.